Re: Find common prefix from a list of strings

die is not the way to normally end execution. And for can iterate a list without indexing.

my $posn = -1;
my $same = 1;
while(defined $same and $posn <= length $files[0]){
 my $chr = substr($files[0], ++$posn, 1);
 for my $name (@files) {  
   undef $same and last if(substr($name, $posn, 1) ne $chr
                                 or length $name < $posn);
 }
}

print 'Prefix is "', substr($files[0], 0, $posn), '"';
[download]

But I can't help but think there's a better way, such as:

# UNTESTED

$max = ( sort { $a <=> $b } map { length } @files )[0];
# length of smallest filename - I hope.

LIST:
for $len ( 1..$max) )
{
    $s = substr($file[0],0,$len);
    last LIST unless scalar grep { /^$s/ } @files == @files;
    # precedence issue here?
}

print "prefix: '",substr($file[0],1,$len-1), "'\n";
[download]

Update: added line to get min length of any filename.

--Bob Niederman, http://bob-n.com

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Re: Re: Find common prefix from a list of strings by Albannach (Monsignor) on Jul 14, 2003 at 19:58 UTC
Drat! Thanks for the reality check - the die was just there for testing, I should have taken it out as it does not add anything, similarly the for was a hold over from an earlier attempt. I've got to proof read my posts more! You obviously have the same must-be-a-better-way (MBABW?) feeling, and I like the idea of the grep trick, though I must admit I usually have a fear of labels. Anyway your code will work with a few minor fixes: `my $s; LIST: for my $len ( 1..length $files[0]) { $s = substr($files[0],0,$len - 1); last LIST unless (scalar grep { /^$s/ } @files) == @files; } chop $s; print "prefix: $s\n";` [download] Update: Not silly at all bobn, I should really have specified that an empty string is the correct answer for no common prefix - thanks for pointing that out. -- I'd like to be able to assign to an luser	[reply] [d/l]
Re: Re: Re: Find common prefix from a list of strings by bobn (Chaplain) on Jul 14, 2003 at 20:05 UTC
Actually, there's one other "bug" - if there are never any matches, I will print out that the prefix is '' - well actually, as a zero-length string, that's actually not untrue, but still silly. --Bob Niederman, http://bob-n.com	[reply]
Re: Re: Re: Find common prefix from a list of strings by bobn (Chaplain) on Jul 14, 2003 at 20:08 UTC
Loved your `chop $s;` - it's the easiest and coolest way to deal with the "I found the condition that makes me stop, but i already added one too many characters" - in fact, I've used it that way myself. --Bob Niederman, http://bob-n.com	[reply]